How Music Effects the Brain

The topic I'd like the research is how music effects the brain. Specifically, when you hear music, what happens? As you must know, music can tigger all sorts of emotions, and change your mood from happy to sad. What tI'd like to know is what causes this sudden change in mood, and why does it happen. I'd also like to research how music can be used as therapy, since music is so in touch with our feelings and emotions. Music is a very big part of my life and something I'm very passionate about, so I'd like the research it.